Gravel-packed wells are commonly used in the well drilling industry. FIG. 1 illustrates one example of a conventional gravel-packed well. In general, after a well borehole B is drilled to an appropriate depth along a centerline axis A, an outer cylindrical casing C is inserted into the borehole B to the full depth of the borehole. A cylindrical screen 10 attached to an inner cylindrical casing (not shown) is then lowered into the outer casing C and centered within the outer casing C via a number of centralizers or centering guides 12 positioned about the perimeter of the screen 10 to define an annular space S between the outer casing C and the screen 10. The annular space S between the outer casing C and the screen 10 is then filled with gravel pack material G and/or another type of filter pack material which fully surrounds the screen 10. During the filling process, the outer casing C may be gradually pulled back until the annular space S is filled to a desired pack depth above the top end of the screen 10.
Following initial placement of the gravel pack G, a development process may be initiated to clear the gravel pack G of fine sand or other unwanted materials and/or to clean up the contact surface between the gravel pack G and the surrounding native soils NS. Some development processes include passing compressed air through the gravel pack G, although other development procedures may also be used. During the development process, some settlement of the gravel pack G may occur, thereby requiring the addition of more gravel/filter media to maintain a pack depth above the top end of the screen 10. Once the gravel pack G is fully developed, the well bore space above the gravel pack G is sealed by a removable sealing apparatus or cap 14 that is lowered down through the outer casing C and into engagement with the upper end of the screen 10. The sealing apparatus illustrated in FIG. 1 includes a seal ring or packer 16, an upper neoprene or rubber seal 18a positioned between the inner diameter of the outer casing C and the outer diameter of an upper portion of the packer 16, and a lower neoprene or rubber seal 18b positioned between the inner diameter of a lower portion of the packer 16 and the outer diameter of an upper portion of the screen 10 (or the outer diameter of an annular flange or length of leader pipe attached to the upper portion of the screen 10).
In the illustrated embodiment, the packer 16 is provided with an upper cylindrical region 16a which supports the upper seal 18a, a lower cylindrical region 16b which abuts or supports the lower seal 18b, and a conical/tapered transition region 16c extending between the upper and lower cylindrical regions 16a, 16b. However, other types and configurations of packers may be used. The upper region 16a of the packer 16 may be removable attached to a support pipe or tether (not shown) to facilitate lowering of the packer 16 through the outer casing C and into position atop the upper portion of the screen 10. The upper region 16a may be removably attached to a support pipe via a bayonet-type attachment, a latch pin/hook arrangement, or other types of attachment mechanisms. The lower region 16b of the packer 16 may be removably attached to the upper end of the screen 10 (or to the annular flange or lead pipe if used) via a bayonet-type attachment, a hook/latch pin attachment, or other types of attachment mechanisms.
The devices and methods used in the conventional gravel-packed well illustrated in FIG. 1 suffer from various problems and drawbacks. For example, during initial construction of the well, it is difficult to maintain the gravel pack G in place, particularly while developing the gravel pack G via the use of compressed air (i.e., a portion of the gravel pack G may be blown out during the developing process). In order to address this concern, a lengthy leader pipe is sometimes added to the top end of the screen 10 to overcome buoyancy of gravel pack G caused by the addition of compressed air. However, the addition of a lengthy leader pipe adds to the overall cost of the well. Additionally, during the gravel pack filling process, it can be difficult to measure the level/depth of the gravel pack G, thereby risking underfilling or overfilling of the annular space S surrounding the screen 10.
Furthermore, over a period of time, most gravel-packed wells must be cleaned and redeveloped. During the aging period of a well, several feet of the gravel pack G may be lost to attrition. If the lost gravel pack G is not replaced, the native soils NS surrounding the annular space S or sands may envelope the portion of the screen 10 that is no longer surrounded by the gravel pack G and may intrude the well (i.e., contaminating the water supply provided by the well). In order to add additional gravel or filter material to the annular space S surrounding the screen 10 to replace the gravel pack lost to attrition, the packer 16 must be disengaged from the screen 10 and temporarily removed from the well via displacement up through the outer casing C. However, removal of the packer 16 can be difficult as the seals 18a, 18b may be torn off during removal and/or the packer 16 may become wedged/lodged within the outer casing C during removal due to the absence of the upper seal 18a and/or due to formation of a thick layer of rust along the inner surface of the outer casing C, thereby hindering or halting the removal process and the gravel refill process. As should be appreciated, if the packer 16 becomes lodged or stuck within the outer casing C, removal can be expensive and time consuming. Moreover, removal of the packer 16 from the screen 10 and/or displacement of the packer 16 through the outer casing C may be hindered or prevented if the screen 10 and the outer casing C are not centered/aligned in the well. Removal of the packer 16 from the screen 10 and/or displacement through the outer casing C can be quite difficult given that most wells are, at least to some extent, crooked or out of vertical alignment, the likes of which can be caused by initial misalignment of the components during installation or gradual shifting of the components over time. Also, removal of the packer 16 from the screen 10 can cause the screen 10 to shift and become misaligned/mis-centered within the well during the refill process since the screen 10 will no longer be fully supported within the well, thereby complicating or preventing reattachment of the packer 16 to the screen 10 after refilling and redeveloping is complete. Additionally, the mechanisms used to attach the packer 16 to the screen 10 and/or to the support pipe/tether can tear away and/or corrode to such an extent as to make reattachment difficult if not impossible, thereby further hindering or preventing removal of the packer 16.
Thus, there remains a need to provide improved devices and methods for adding/refilling gravel or filter pack material to a well. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.